Jeanne N. Jodoin

Regulation of dynein localization and centrosome positioning by Lis-1 and asunder during Drosophila spermatogenesis

Dynein, a microtubule motor complex, plays crucial roles in cell-cycle progression in many systems. The LIS1 accessory protein directly binds dynein, although its precise role in regulating dynein remains unclear. Mutation of human LIS1 causes lissencephaly, a developmental brain disorder. To gain insight into the in vivo functions of LIS1, we characterized a male-sterile allele of the Drosophila homolog of human LIS1. We found that centrosomes do not properly detach from the cell cortex at the onset of meiosis in most Lis-1 spermatocytes; centrosomes that do break cortical associations fail to attach to the nucleus. In Lis-1 spermatids, we observed loss of attachments between the nucleus, basal body and mitochondria. The localization pattern of LIS-1 protein throughout Drosophila spermatogenesis mirrors that of dynein. We show that dynein recruitment to the nuclear surface and spindle poles is severely reduced in Lis-1 male germ cells. We propose that Lis-1 spermatogenesis phenotypes are due to loss of dynein regulation, as we observed similar phenotypes in flies null for Tctex-1, a dynein light chain. We have previously identified asunder (asun) as another regulator of dynein localization and centrosome positioning during Drosophila spermatogenesis. We now report that Lis-1 is a strong dominant enhancer of asun and that localization of LIS-1 in male germ cells is ASUN dependent. We found that Drosophila LIS-1 and ASUN colocalize and coimmunoprecipitate from transfected cells, suggesting that they function within a common complex. We present a model in which Lis-1 and asun cooperate to regulate dynein localization and centrosome positioning during Drosophila spermatogenesis.

Asunder is a critical regulator of dynein-dynactin localization during Drosophila spermatogenesis.

Spermatogenesis uses mitotic and meiotic cell cycles coordinated with growth and differentiation programs to generate functional sperm. Our analysis of a Drosophila mutant has revealed that asunder (asun), which encodes a conserved protein, is an essential regulator of spermatogenesis. asun spermatocytes arrest during prophase of meiosis I. Strikingly, arrested spermatocytes contain free centrosomes that fail to stably associate with the nucleus. Spermatocytes that overcome arrest exhibit severe defects in meiotic spindle assembly, chromosome segregation, and cytokinesis. Furthermore, the centriole-derived basal body is detached from the nucleus in asun postmeiotic spermatids, resulting in abnormalities later in spermatogenesis. We find that asun spermatocytes and spermatids exhibit drastic reduction of perinuclear dynein-dynactin, a microtubule motor complex. We propose a model in which asun coordinates spermatogenesis by promoting dynein-dynactin recruitment to the nuclear surface, a poorly understood process required for nucleus-centrosome coupling at M phase entry and fidelity of meiotic divisions.

Human Asunder promotes dynein recruitment and centrosomal tethering to the nucleus at mitotic entry

Proper coupling of centrosomes to the nuclear surface at prophase is essential for fidelity of mitotic events. A pool of dynein motors anchored to the nuclear surface mediates this step. The protein Asunder is required in human cultured cells for dynein localization and tethering of centrosomes to the nucleus at mitotic entry.

Nuclear-localized Asunder regulates cytoplasmic dynein localization via its role in the Integrator complex

A pool of dynein anchored to the nuclear surface mediates many processes at G2/M, although its spatial and temporal regulation is poorly understood. Asunder, a critical regulator of dynein recruitment to the nuclear envelope, works in the nucleus as part of Integrator, an snRNA-processing complex, to mediate this event.

Abl suppresses cell extrusion and intercalation during epithelium folding

Apical constriction drives tissue folding or cell extrusion in different contexts, but the mechanisms that dictate the specific outcomes are poorly understood. Live imaging shows that Abl has a critical role in inhibiting cell extrusion during tissue folding by promoting apical–basal polarity and adherens junction positioning.

The snRNA-processing complex, Integrator, is required for ciliogenesis and dynein recruitment to the nuclear envelope via distinct mechanisms.

Summary We previously reported that the small nuclear RNA processing complex, Integrator, is required for dynein recruitment to the nuclear envelope at mitotic onset in cultured human cells. We now report an additional role for INT in ciliogenesis. Depletion of INT subunits from cultured human cells results in loss of primary cilia. We provide evidence that the requirements for INT in dynein localization and ciliogenesis are uncoupled: proteins essential for ciliogenesis are not essential for dynein recruitment to the nuclear envelope, while depletion of known regulators of perinuclear dynein has minimal effects on ciliogenesis. Taken together, our data support a model in which INT ensures proper processing of distinct pools of transcripts encoding components that independently promote perinuclear dynein enrichment and ciliogenesis.

Characterization of a cdc14 null allele in Drosophila melanogaster

ABSTRACT Cdc14 is an evolutionarily conserved serine/threonine phosphatase. Originally identified in Saccharomyces cerevisiae as a cell cycle regulator, its role in other eukaryotic organisms remains unclear. In Drosophila melanogaster, Cdc14 is encoded by a single gene, thus facilitating its study. We found that Cdc14 expression is highest in the testis of adult flies and that cdc14 null flies are viable. cdc14 null female and male flies do not display altered fertility. cdc14 null males, however, exhibit decreased sperm competitiveness. Previous studies have shown that Cdc14 plays a role in ciliogenesis during zebrafish development. In Drosophila, sensory neurons are ciliated. We found that the Drosophila cdc14 null mutants have defects in chemosensation and mechanosensation as indicated by decreased avoidance of repellant substances and decreased response to touch. In addition, we show that cdc14 null mutants have defects in lipid metabolism and resistance to starvation. These studies highlight the diversity of Cdc14 function in eukaryotes despite its structural conservation. Summary: The Cdc14 phosphatase has been implicated in cell cycle regulation in S. cerevisiae. We show that Drosophila cdc14 mutants are viable, but exhibit defects in sperm competition, chemosensation, and mechanosensation.

Epithelial Contractility: A Crowning Achievement

Epithelial cells transmit contractile force with adherens junctions to mediate morphological changes like the extrusion of apoptotic cells. In this issue of Developmental Cell, Michael and colleagues (2016) show that the actin binding protein Coronin plays a critical role in actin cytoskeleton reorganization and association with junctions to promote contractility.